Conventionally, personal computers (PCs), i.e., notebook PCs or laptop PCs have been used by placing them on desks. It has therefore been possible to obtain satisfactory antenna performance by mounting an antenna 102 above a liquid crystal display (LCD) 104 as illustrated in FIG. 1A.
In recent years, tablet PCs, such as the one illustrated in FIG. 1B, have been introduced into the market. The tablet PC is held by hand when in use. In this case, when the user's hand is placed in contact with the mounting portion of the antenna 102, the antenna performance drops. Further, when the user tilts the PC when in use, the antenna performance drops.
Similar problems also occur with notebook PCs as size reductions are made. On the other hand, a convertible PC having a 180-degree rotatable LCD and transformable from a notebook to a tablet PC and vice versa has been introduced into the market. Antenna performance degradation also becomes a problem with the convertible PC.
One possible approach to addressing the problem of antenna performance degradation is to mount a plurality of antennas 102 as diversity antennas, as illustrated in FIGS. 2A and 2B, and to receive data from one of the antennas that provides the best performance. By providing, for example, as many receive circuits as there are antennas and by detecting the received signal strength from each antenna and selecting the appropriate receive circuit, good communication quality can be maintained (refer, for example, to patent documents 1 and 2 listed below). However, the cost increases because this configuration requires the provision of as many receive circuits as there are antennas.
Another possible approach, which eliminates the need to provide as many receive circuits as the number of antennas, is to sequentially select the antennas for connection to the receive circuit and detect the received signal strength from each antenna (refer, for example, to patent documents 3 to 5 listed below). However, in this configuration, it takes time to select the receiving antenna because switching has to be made from one antenna to another in sequence.
Patent document 1: Japanese Unexamined Patent Publication No. 2006-245801
Patent document 2: Japanese Unexamined Patent Publication No. 2007-235305
Patent document 3: Japanese Unexamined Patent Publication No. 2005-142866
Patent document 4: Japanese Unexamined Patent Publication No. 2005-130175
Patent document 5: Japanese Unexamined Patent Publication No. H11-150490